System for the transmission of oscillations



May 20, 1941. J. COLLARD ET AL 2,242,379

SYSTEM FOR THE TRANSMISSION OF OSCILLATIONS Filed Jan. 11, 1940 Fig. 3.

Z0 0 vww C R1 L13 R 23 L In ve/zffl/vy I 6211 041 mffififsr Patented May 20, 1941 SYSTEM FOR THE TRANSMISSION OF OSCILLATIONS John Collard, Hammersmith, London, and John Edward Best, West Ealing, London, England, assignors to Electric & Musical Industries Limited, Hayes, Middlesex, England, a company of Great Britain Application January 11, 1940, Serial No. 313,372 In Great Britain November 4, 1938 20 Claims.

This invention relates in general to wave transmission systems, but more particularly, though not exclusively, to electric signal transmission systems.

The properties of any wave transmission path in which in a specific frequency range the constants are substantially smoothly distributed are known when the complex propagation constant is determined for all frequencies within the specified range where a is the attenuation constant and p the phase constant and where R, L, G and C are respectively the resistance, inductance, leakance and capacity, or are effectively so, of the transmission path per unit length and w is the angular frequency of the signals being transmitted. If the attenuation constant on is independent of frequency then all oscillations caused to travel over the path will do so without the occurrence of variations in relative amplitude. If also the phase constant c is proportional to 0.1 so that the time delay per unit length,

is constant, then relative phases will also be transmitted undisturbed.

In general, with a cable or transmission line these conditions are not satisfied and it is necessary therefore to employ equalising or compensating circuits whereby the attenuation constant is made effectively substantially independent of frequency and the phase constant substantially directly proportional tofrequency over the range of the signals transmitted along the transmission line or cable. The variation with frequency of the loss and phase delay of the transmission line or cable arises either from the variation with frequency of the effective resistance and inductance of the cable or of. the effective capacity and leakance of the cable or from the variation of all of these constants. In the example provided by telephony, variations in phase are relatively unimportant, so that equalising circuits are provided mainly for the purpose of correcting the attenuation or loss characteristic. Some effect on phase is always introduced by the use of such circuits, but its extent is usually small; in some cases, however, it may be sufficiently large to render necessary the addition of phase correcting circuits. These circuits disturb the attenuation equalisation and it may be necessary to add further circuits to correct for this. With these methods it will be seen that the final characteristics of loss and phase are likely to possess a number of superposed and practically unavoidable minor irregularities distributed more or less at random. If a number of such lines happens to be employed in series, these random irregularities may at certain frequencies add upto a very considerable amount.

In transmitting a range of signals, such as occur in television transmissions, along a cable the problem is even more complicated. Not only is it important that variations in relative amplitude should lie within narrow limits, but quite small variations in relative phase are easily noticeable, so that phase variations also require to be compensated with considerable accuracy. From the discussion on the methods of. compensation in telephony, it will be appreciated that their application to compensation with such signals as occur in television is particularly difficult, and it will be seen how, in a long length of cable, it is practically impossible so to proportion the various circuits that large superposed variations of irregular or random character do not occur in the characteristics, either of loss or of phase delay.

The present invention is concerned with the simultaneous equalisation of the loss and phase characteristics of a cable or a transmission line, by which the difficulties referred to above are substantially overcomef but, as will be apparent hereinafter, the invention is capable of a much wider application.

The invention in one aspect is concerned with the elimination of those variations of attenuation and phase delay with frequency, giving rise to distortion, that occur due to skin effect in the conductors, by reason of which the resistance of the cable increases with frequency and the inductance falls. In another aspect it may also be applied to remove the distortion that arises from the presence of, a dielectric between the conductors, which causes the capacity to decrease slightly and the leakance to increase as the frequency rises.

In the specification of U. S. Patent No. 2,158,978 methods of and means for achieving these various objects were described in which a number of equaliser sections forming an equaliser network were so arranged and: constructed that their characteristic or reference frequencies, as therein defined, were distributed according to a law of equal spacing. It has, however, since then been found that a [certain law of variable spacing may equally well be employed for the attainment of the same objects. Thus, as in the aforesaid specification,

.tions of one object of the invention is to provide an improved transmission system in which the variation of loss and phase delay due to variation with frequency of. the effective resistance and inductance or capacity and leakance, or both (or their analogues) is simultaneously equalised and in which the equalisation is substantially not subject to superposed irregularities of a random character. 7 means are described for attaining this object,

As in the aforementioned specification, what is meant by equalisation of loss and phase delay is that the attenuation constant ismade effectively substantially independent of frequency and the phase constant is made effectively substantially directly proportional to frequency over the range of frequencies for which equalisation is effected. Y

The invention may be employed withany suitable type of equaliser section provided that the equaliser sections used possess characteristic curves with respect to attenuation and phase displacement; which can be expressed as funcwhere p is an angular frequency defined in the same way for all sections employed and w is the angular frequency at which either of these properties expressed by the characteristic curves is evaluated. As in the aforementioned specification the frequency'p will hereinafter be referred to as the reference frequency. In section of the simple type comprising series arms com- 7 posed of inductances in series with resistances, a

' ence frequenciescorrespond to a'distribution-law which may be deduced when the characteristics of the transmission path are known;

.The invention is applicable for equalising simultaneously loss and phase delay in all transmissionpaths forwhich the loss characteristic may be expressed as the sum of a number of terms of the form AM)", and for which the phase characteristic possesses a number of corresponding terms of the form Baa, where n is'always less than unity and 1 B =A tan These conditions are found experimentally to be satisfied generally by cables such as are employed for example, in the transmission of television sigrials. The invention may be applied to other transmission paths, such as those in which mechanical or acoustical oscillations are required tobe transmitted, provided the above conditions are satisfied by the path; it is well known that the analogues of resistance, inductance, capacity and leakance exist in mechanical and acoustical transmission systems. The invention may also be employed, when the abovementioned relation between An and En does not holdlto ,correct'any attenuation characteristic or any phase characteristic which is analysable into a finite series of terms vof, the form Xnw" provided In this specification, however, new

the values of n lie all below certain respective upper limits. More broadly the invention may be applied to provide a frequency characteristic simulating substantially any desired frequency characteristic provided this characteristic may be expressed as a finite power series of terms such as Xnw" in which 12 does not exceed a certain limiting value.

The present invention according to one feature, comprises a wave transmission system ineluding a transmissionpath along which oscillations extending over a range of frequencies are caused to travel, in which the path is such as to introduce distortion of said signals and in which said distortion corresponds to a frequency characteristic F(w) of the form of two or more terms of the form Xnw where w/21r is the frequency of said oscillations and n is limited to values less than two if F(w) represents loss or to values less than unity if F(w) represents phase delay and ra oompensating or equalising path associated with said transmission path formed by the connectio'nin series of a plurality of equaliser sections having reference frequencies 111, In, 103 J pr distributed in such a way as to correspond to a series of slowly or evenly varying differences F(pr+1) F(pr whereby said distortion of said signals is substantially compensated in said range of frequencies.

According to another feature of the invention, a wave transmission system is provided comprising a transmission path along which oscillations extending over a range of frequencies are caused to travel, in which the path is such as to introduce distortion of said signals owing to the variation with frequency of the efiective resistance and inductance or thecapacity and leakance or both (or their analogues), and in which said distortion corresponds to a frequency characteristic F-(w) 'of the form of two or more terms of the form Xnw" where w/21r is the frequency of said oscillations and n is limited to values less than two if F0) represents loss or to values less than unity if F(w) representsphase delay and atompensating or equalising path associated with said transmission path formed by the connection in series of a plurality of equaliser sections having reference frequencies 101, pa, n pr distributed in such a way as to correspond to a series; of slowly or evenly varying differences F(pr+1)F(p1) whereby said distortion of said signals owing to the variation with frequency of the effective resistance and inductance or the capacity and leakance or both, either with respect to loss or-phase delay or to both simultaneously when all values of n are limited to less than unity, is substantially compensated in said range of frequencies. According to another feature of the invention there is provided means for simulating a predetermined frequency characteristic F(w) lying within a predetermined range of frequencies and ofthe form of two or more terms of the form X'nw where i /2 is the'frequency and n is limited to values less thantwo if F(w) represents loss or to Values less than unity if F(w) represents phase delay comprising a plurality of sections which connected in series form said transmission path and which possess reference frequencies 111, 122, p3 pr so distributed as to correspond to a series of slowly or evenly varying differences F(pr+i) -F(Pr) whereby said transmission path possesses a frequency characteristiowhich simulates substantially said predetermined characteristic.

if desired, a number of groups of sections are employed, the reference frequencies of the sections in each group being distributed with a slowly or evenly varying spacing and the sections of the different groups being of different types.

It will be appreciated that the present invention may be applied in conjunction with the aforementioned specification to provide'a network partly constructed on the principle of variable loss spacing and partly on the principle of constant loss spacing for individual power terms.

The present invention is especially applicable to an electric signal transmission system which is designed for the transmission of signals extending over a very wide frequency range; for example, a range extending at least up to 100 kilocycles per second. The invention is also applicable to the case in which the transmission line is designed for the transmission of frequencies from substantially zero frequency up to about two to three megacycles per second, such latter frequencies being ordinarily encountered in the transmission of television signals. When dealing with signals extending over such a wide range of frequencies the variation of loss and phase delay is due to variation with frequency of all four primary constants of the cable and the present invention can accordingly be applied to such a system for equalising simultaneously the greater part of the variation of the loss and phase. The invention may also be applied to transmission lines or cables transmitting signals extending over much smaller frequency ranges. It may also be employed for equalising in a transmission line or cable the effect only of variation with frequency of the resistance and inductance or capacity and leakance. It is also possible as stated in the aforesaid specification to apply it to a cable at intervals along its length, which intervals are short compared with the wavelength of the highest frequency to be transmitted, or to the case in which an arbitrary length of cable or transmission line is equalised as a whole by the use of a plurality of equaliser sections forming an artificial line disposed at any suitable position in the transmission path.

Subject to the conditions set out in the previous specification, any type of equaliser section may be employed in the invention. Sections which are suitable for use in the present invention for equalising a cable are shown by way of example in Figures and 6 of patent specification of U. S. 2,158,978. For simulating generally these sections or their inverses, or the sections shown in Figure 4 of said patent specification, or other types of sections may be used. Preferably the invention employs sections of the socalled constant resistance type, but it is not limited in its scope to the use of such sections.

The principle upon which the invention is based will now be more fully elucidated. Let

tions, there being assigned to each section a definite value of p; thus let represent the loss characteristic of the section where K is the loss of the sec-tion at zerofrequency. Suppose that in a frequencyrange dp located at the frequency p there occurs a numher MQD) dp of such values of p. Then the variable part of the loss due to all of the aforementioned sections is given by the summation covering all of the sections. It is, however, possible to expand the function M(p) as a power series in p; thus it is possible to set If this is done, then it follows that the loss (in becomes expressible as the series which is a power series in w, the function Sm) being the integral where a( w)=E1LA1Lw"; n 2 is the required cornpensating characteristic.

That such a distribution corresponds to a slowly varying spacing with respect to loss if there are more than one of the terms Anw" may be seen as follows. The characteristic may be simulated by means of a frequency distribution given by C n-1 n (P) i. e., by means of a frequency spacing equal to L Y N (2 The spacing with respect to loss on the characteristic F(p) corresponding to this is (p) N (p) where a dash denotes differentiation. loss spacing is Hence the 2,,nC,,p"

c nl W) from which it is clear that a:(p) varies in a slowly varying manner with the variable p.

Corresponding to a loss provided by a number of sections distributed according to (q) being the phase displacement of a single section and corresponding to (q). Thus, not

only may the distribution lvfiplbe employed to neutralise all the terms in the expression for the loss of a cable, but it follows that the phase delay of the cable may be equalised at the same time if it possesses a phase characteristic negative of that given by the abov expression for [8(w) The integrals sm) and TM) are integrated over a range corresponding at least to a range including all the values of p of the various respective sections. This range amounts in effect to an integration extending overall values of q between zero and finity. In the previous aforementioned specification it wasshown how these integrals can be evaluated. In particular it was shown that w V m)? when j(q) and (q) are the characteristics of any constant resistance section. Ityhas been found, however, by experiment that the phase termsthatarise corresponding to this ratio and to loss terms And! are substantially of the same magnitude as those arising in a typical practical cable possessing a loss given by the terms Am"; in such cases, therefore, a single equaliser constructed according to the principles set out above can be utilised to correct simultaneously for phase and amplitude distortion arising in the course of transmission over the cable. In the afore-mentioned specification, the method was toemploy a number of equalisers each correcting for a single component term Am inthe loss characteristic and a corresponding phase term, and each possessing a constant loss spacing. It will be appreciated, of course, that certain terms may be equalised separately While the remainder may be equalised by a single equaliser according to the methods ofthe present application.

The invention is not limited to the us throughout of a single type of section, namely,'one always described, for example, by f(q). Thus, suppose a number of types "of sections of which the kth type has a loss characteristic fmq) and a distribution function Mk-(p) Znanl,kp

An equaliser formed by these sections can be made to possess a required loss characteristic 21L Anti) if AEkan-i,ksk(rt) Where a. (n fr nc) Gin-1,76 is simply set equal to (Zn-1 so that all the It will be appreciated from the earlier analysis that in all these cases corresponding to every sagas iser there will be a corresponding term in" a",

in the phase characteristic. In a transmission path according to-the above general case corresponding to a lossterm j I H (Q7121: an l,lcsk(n) there will be a phase term w Z1zan1,l cTIc(n) ma l neumoni But a certainothernumber of sections with characteristics Ma) and distributions Ms(p) will also give this result if Lar eMup p that is, they will be equivalent if 21636411) Mup) :zsruq) Mme) If all the sections have the same type of charac teristics, i. e., if

V frtq) --f(q) :Mq)

this "result reduces to. the very simple one, that the total number of sections must be the same in each network in any .given frequency range.

It will be appreciated that in the above analysis .there'are no. special restrictions other than thosegalready mentioned; set upon the type of equaliseri-section that may be'employed; preferably; constantj resistance; sections are employed, but any sectionssatisfying the general requirements set out. in the afore-mentioned prior specification' may be used; sections that have been found particularly suitable are. described therein. It will also be appreciated that though the 'methods described herein are directed principally to some of. its: practicalembodiments the same will new be'describedby way of examplewith reference to the accompanying drawing in which:

Figure 1 shows a transmission system in schematic f-orm comprisingatransmission line and an equalizer network inac'cordance with the present invention for the purposeof equalizing the distortion'l-arisin'g.intransmission along said" line Figure :2 illustrates the nature of the' los's characteristicof the transmissionline of the previous i figure and indicates the manner in which the ref- Thus againerence frequencies of the sections of the equalizer network of that figure are distributed according to the invention;

Figure 3 shows a further loss characteristic which may be equalized in accordance with the invention; and

Figures 4 and 5 illustrate typical sections that may be employed in equalizing loss characteristics of the type shown in Figures 2 and 3 respectively or that may be employed in simulating loss characteristics of the type shown in Figures 3 and 2 respectively.

Referring to Figure 1, T is a transmitter and may send, for example, television signals covering a frequency range from zero or substantially zero frequency up to say two megacycles per second or more over the transmission line L which has an attenuation characteristic F(w) of the form indicated in Figure 2. The distorted signals which arrive at the end of the transmission line L are fed into the compensating or equalizing network C and after correction in this network they are fed to the receiver R. The network C is composed of a very large number of sections, of the type shown, for example, in Figure 4, which have a substantially identical zero-frequency loss that is comparatively small and is of the order of three decibels and which have losses equal to half of this at certain other frequencies. The various sections are so constructed that these frequencies, the reference frequencies of the sections, form a finely graded sequence n, 112, 1):, p4, extending from the low-frequency end of the transmitted range of signals .to frequencies higher than the highest transmitted. As shown in Figure 1 the sections N1, N2, N3, N4, are arranged in the order of the above sequence, but this is of course not necessary and they may be arranged in any order provided that there are no appreciable changes in characteristic impedance from section to section.

Figure 2 shows how the reference frequencies 101, 122, 103, p4, are distributed. In a typical case in practice the line L might have a Variable part of loss as distinct from its zero-frequency loss representable substantially by a pair of terms, one proportional to the square root of frequency and the other linear in frequency. Consequently, it is necessary to provide an equalizing network that will simulate apart from zero frequency loss a loss characteristic of this form:

It follows from the analysis that has previously been given that the necessary loss-spacing function (p) is of the form:

where in fact:

1 K=S )S(l) In the above K, b, c and at each are constants; 8(1/2) and 3(1) are the values of the integral of SW), if n is set equal to 1/2 and 1, respectively,,while C1 2 and C1 are coefficients in ex- 7 pansion. At very low frequencies (p) tends to the value Ka/c; at very high frequencies it tends to Kb/d; in betweenit varies in accordance with the above formula between these limits. In Figure 2 the spacings at the low frequencies, for example:

are of the order of the lower frequency limit just mentioned; at the high-frequency end of the characteristic they are of the order of or are tending to the high frequency limit; intermediately they are varying slowly between the two limits. Equalization of loss as shown in Figure 3 can be carried out in like general manner.

Figure 4 illustrates a preferred form of equalizer section for use in the network C of Figure 1. Essentially it consists of a series arm comprising the condenser C11 shunted by the resistance R12 to which inverse with respect to the characteristic impedance Z0 are the shunt-arm elements, the inductance L21 and the resistance R22 connected in series. These elements give a generally falling loss characteristic, the fall of which is made more rapid at higher frequencies, by the inclusion of the inductance L13 in series with the resistance R12 in the series-arm and by the inclusion of its inverse element, the condenser C23, shunted across the resistance R22. The resistance Z0 is connected across the series-arm so that the section possesses the constant characteristic impedance of Z0 at all frequencies.

Figure 5 shows the inverse network to that just described and this may be employed when equalizing loss characteristics of the type shown in Figure 3. In both networks the shunting resistance Z0 may, as an alternative, be connected in series with the shunt arm. As already mentioned a network formed of sections such as those illustrated in Figure 4-. may be constructed to simulate any loss characteristic of the type shown in Figure 2, while sections of the type shown in Figure 4 may be used for simulating loss characteristics of the form of that in Figure 3.

In Figure 5 the essential series-arm elements are the inductance L11 and resistance R12 which have respectively their inverses in the shunt-arm elements constituted by the condenser C21 and resistance R22, these inverses of course being taken with respect to the impedance Z0. The additional series-arm element formed by the condenser C13 and the additional shunt-arm element formed by the inductance L23, which are inverses of each other with respect to the impedance Z0, are for the purpose of increasing the rapidity of attenuation at the higher frequencies.

In the following claims, what is meant by a transmission path, line or cable of the kind hereinbefore specified, is a transmission path, line or cable in which the loss characteristic of the path, line or cable which introduces distortion and which is to be equalised, can be analysed into one or more component terms of the form Aw" and in which the phase delay characteristic of the path, line or cable can be analysed into one or more component terms of the form:

A,, tan

cables or transmission lines can have, their loss and phase characteristics analysed into the above-mentioned terms.

It will be appreciated that the networks that have been described are not limited to equalising the characteristics of a cable since suitably constructed they may be used for simulating such characteristlcscr other given characteristics.

We claim:

1. A wave transmission system including a transmission path along which oscillations extending over a'range of frequencies are caused to travel and in which range the attenuation of. said path varies with the frequency a: substantially as the sum PM) of. at least two terms of the form AW? and the phase delay of said path varies substantially as the sum of atleast two terms of the form A tan mnw 7 said magnitudes Anand 'n to be determined by analysis of the characteristics of the transmission path, said variations causing distortion, and a compensatingpath associated with saidtransmissionpath comprising a plurality of equaliser sections having the same attenuation at zero fre quency and attenuations at certain differing reference frequencies 101, 102, p3 p1- equal to said attenuation at zero frequency multiplied by'an arbitrary factor, said different reference frequencies being allotted 'to said sections and therebyvdistributed in such a way as to correspond to, a series of slowly or evenly varying differences of two functions F(p1+1)F(pT),

thereby substantially equalizing simultaneously said variations of attenuation and. phase delay causing distortion. 7 V

2.,A wave transmission system including a transmission path along which oscillations exform 1 A tan mr. to"

said magnitudes An and n to be determined by analysis of, the characteristics of the transmis-f sion .path,,said variations causing distortion, and

" a compensatingrpath associated with said transmission path comprising a plurality of equaliser sectionshaving the same attenuation atrzero frequencyand attenuations at certain differing referencefrequencies 911, p2, p3 pr equal to said attenuation at zero frequency multiplied by an arbitrary factor, said difference reference frequencies being allotted to said sections and there! by distributed in such. a way as to correspond to a series of slowly or evenly varying differences of two functions F(pr+1)-F('pr), thereby substantially equalising simultaneously said variations of attenuation and phase delay causing distortion due to, said variation withofrequency of the-effective inductance and resistance of said path.

3. A wave transmission system including a transmission path along which oscillations extending over a range of frequencies are caused to travel and in which range owing to the variation with frequency of the effective capacity and leakanceof said path the attenuation of said path varieswithe the" frequency to substantially as the sum,F(w) of atleast two terms of the form Ana! and the phase delay of said'path varies substantially as the sum of at least two terms of the form A tan gimme)" said magnitudes An and n to be determined by analysis of the characteristics of the transmission path, said variations causing distortion, and a compensating path associated with said transmission path comprising a plurality of equaliser sections having the same attenuation at zero frequency and attenuation at certain differing reference frequencies Zn, 102, p3 pr equal to said attenuation at zero frequency multiplied by an'arbitrary factor, said different reference frequencies being allotted to said sections and thereby distributed in such a way as to correspond to a series of slowly or evenly varying differences of two functions F(pr+1)-F(pr), thereby substantially equalising simultaneously said variations of attenuation and phase delay causing distortion due to-said variation with frequency of the eflective-capacity and leakance ofsaid path.

4." A wave transmission system including a transmission path along which oscillations extending over arange of frequencies are caused to travel and in which range owing to the variation withfrequency of the effective inductance, resistance, capacity and leakance of said path the attenuation of said path varies with the frequency or substantially as the sum F00) of at least two terms ofithe form Anw and the phase delay of said path varies substantially as the sum of at least two. terms of the form l A tan nnate" said magnitudes A11. and n to be determined by analysis of the characteristics of the transmission path, said variations causing distortion, and a compensating path'associ-ated with said transmission path comprising a plurality of equaliser sections having the same attenuation at zero frequency and attenuations at certain differing reference frequencies 121, 102, p3 pr equal to said attenuation at zero frequency multiplied by an arbitrary factor, said different reference frequencies being allotted to said sections and thereby distributed in such a way as to correspond to a series of slowly or evenly varying differences tions of attenuation and phase delay causing distortion due to said variation with frequency of r the effective inductance, resistance, capacity and leakance of said path.

5. A wave transmission system including a transmission path along which oscillations extending over a range of frequencies are caused to travel and in which range the attenuation of said path varies with the frequency to substantially as the sum F(w) of at least two terms of the form Aw, said magnitudes An and n to be determined by analysis of the characteristics of the transmission path, said variations causing distortion, and a compensating path associated with said transmission path comprising a plurality of equaliser sections having the same attenuation at zero frequency and attenuations at certain differing refence frequencies 121, 102, p3 pr equal to said attenuation at zero frequency multiplied by an arbitrary factor, said different reference frequencies being allotted to said sections and thereby distributed in such a way as to correspond to a series of slowly or evenly varying differences of two functions F(I)r+1)--F(Z)r), thereby substantially equalising simultaneously said variations of attenuation causing distortion.

6. A wave transmission system including a transmission path along which oscillations extending over a range of frequencies are caused to travel and in which range owing to the variation with frequency of the effective inductance and resistance of said path the attenuation of said path varies with the frequency or substantially as the sum F(w) of at least two terms of the form Ano said magnitudes A11. and n to be determined by analysis of the characteristics of the transmission path, said variations causing distortion, and a compensating path associated with said transmission path comprising a plurality of equaliser sections having the same attenuation at zero frequency and attenuations at certain differing reference frequencies 101,112,103 pr equal to said attenuation at zero frequency multiplied by an arbitrary factor, said different reference frequencies being allotted to said sections and thereby distributed in such a way as to correspond to a series of slowly or evenly varying differences of two functions F(1Dr+1)--F(1Ur), whereby substantially equalising simultaneously said variations of attenuation causing distortion due to said variation with frequency of the effective inductance and resistance of said path.

7. A wave transmission system including a transmission path along which oscillations extending over a range of frequencies are caused to travel and in which range owing to the variation with frequency of the effective capacity and leakance of said path the attenuation of said path varies with the frequency 01 substantially as the sum Fm) of at least two terms of the form Anw'", said magnitudes An and n to be determined by analysis of the characteristics of the transmission path, said variations causing distortion, and a compensating path associated with said transmission path comprising a plurality of equaliser sections having the same attenuation at zero frequency and attenuation at certain differing reference frequencies 1101, 102, pa pr equal to said attenuation at zero frequency multiplied by an arbitrary factor, said different reference frel quencies being allotted to said sections and thereby distributed in such a Way as to correspond to a series of slowly or evenly varying differences of two functions F(pr+1)F(pT), thereby substantially equalising simultaneously said variations of attenuation causing distortion due to said variation with frequency of the effective capacity and leakance of said path.

8. A wave transmission system including a transmission path along which oscillations extending over a range of frequencies are caused to travel and in which range owing to the variation with frequency of the effective inductance, resistance, capacity and leakance of said path the attenuation of said path varies with the frequency or substantially as the sum F(w) of at least two terms of the form Aw", said magnitudes An and n to be determined by analysis of the characteristics of the transmission path, said variations causing distortion, and a compensating path associated with said transmission path comprising a plurality of equaliser sections having the same attenuation at zero frequency and attenuation at certain differing reference frequencies :21, 102, p3 pr equal to said attenuation at zero frequency multiplied by an arbitrary factor, said different reference frequencies being allotted to said sections and thereby distributed in such a way as to correspond to a series of slowly or evenly varying differences of two functions F(pr+1)-F(p1), thereby substantially equalising simultaneously said variations of attenuation causing distortion due -to said variation with frequency of the effective inductance, resistance, capacity and leakance of said path.

9. A wave transmission system including a transmission path along which oscillations extending over a range of frequencies are caused to travel and in which range the phase delay of said path varies substantially as the sum F(w) of at least two terms of the form Bnw", said magnitudes B and n determined by analysis of the characteristics of the transmission path, said variations causing distortion, and a compensating path associated with said transmission path comprising a plurality of equaliser sections having phase delays equal to a single arbitrary value at certain differing reference frequencies 111, 122, p3 pr said different reference frequencies being allotted to said sections and thereby distributed in such a way as to correspond to a series of slowly or evenly varying differences of two functions F'(pT+1)F(p,), thereby substantially equalising simultaneously said variations of phase delay causing distortion.

10. A wave transmission system including a transmission path along which oscillations extending over a range of frequencies are caused to travel and in which range owing to the variation with frequency of the effective inductance and resistance of said path the phase delay of said path varies substantially as the sum F(w) of at least two terms of the form Bnw", said magnitudes B and n determined by analysis of the characteristics of the transmission path, said variations causing distortion, and a compensating path associated with said transmission path comprising a plurality of equaliser sections having phase delays equal to a single arbitrary value at certain differing reference frequencies 101, 122, pa pr said different reference frequencies being alotted to said sections and thereby distributed in such a way as to correspond to a series of slowly or evenly varying differences of two functions F(pT+1)F(p1-), thereby substantially equalising simultaneously said variations of phase delay causing distortion due to said variation with frequency of the effective inductance and resistance of said path.

11, A wave transmission system including a transmission path along which oscillations extending over a range of frequencies are caused to travel and in which range owing to the variation with frequency of the effective capacity and leakance of said path the phase delay of said path varies substantially as the sum F(w) of at least two terms of the form Bnw", said magnitudes B and n determined by analysis of the characteristics of the transmission path, said variations causing distortion, and a compensating path associated with said transmission path comprising a plurality of equaliser sections having phase delays equal to a single arbitrary value at certain differing reference frequencies 201, 1 2, 20s

pr said different reference frequencies being allotted to said sections and thereby distributed in such a way as to correspond to a series of slowly or evenly varying differences of two functions F(pT+1)F(p1), thereby substantially equalising simultaneously said variations of phase delay causing distortion'due to, said'yariation Withfrequency of. the effective capacity andzleakance of said path.

12. A wave transmission system including a transmission path along which oscillations extending over a range of frequencies are caused to travel and in which range owing to the variation with frequencyof the effective inductance, resistance, capacity and leakance of said path the phase delay of said path varies substantially as the sum F(w) of at least two terms of the form Baa, said magnitudes B and n determined by analysis of the characteristics oft-he transmission path, said variations causing distortion, and a compensating path associated with said transmission path comprising a plurality of equaliser sectionshaving phase delays equal to a single arbitrary value at certain differing reference frequencies 121,792, p3 pr said different reference frequencies being allotted to said sections and thereby distributed in such a way as to correspond to a series of slowly or evenly varying differences of two functions F(pr+1)F(Dr) thereby substantially equalising simultaneously said vari-l ationsof phase delaycausing distortion due to said variation with frequency of theeifective inductance, resistance, said path.

13. A wave transmission system, particularly for television, including a transmission path as exemplified by a cable along which oscillations capacity and leakance of extending over a range of frequencies up to at,

least 100' kilocycles per second are caused to travel, and in which range the attenuation of said path varies with the frequency or substantially as the sum Fm) of at least two terms of the form Ana and the phase delay of said path varies substantially as the sum of at least two terms of the form lA tan Tuna) said magnitudes An andn to be determined by analysis of the characteristics of the transmission path, said variations causing distortion, and a compensating path associated with said transmission path comprising a plurality of equaliser sections having the same attenuation at zero fre-v quency and attenuations'at certain diifering'reference frequencies 121,102, p3 pr said attenuation at zero frequency multiplied by an arbitrary factor, said diiferent reference frequencies being allotted to said sections and thereby distributed in such a way as to correspond to a series of slowly or evenly varying differences of two functions F(pr+1)F(pv), thereby substantially equalising simultaneously said variations of varies substantially as the sum of at least two of the form A tan nmw" said magnitudes An and n to be determined by analysis of the characteristics of the transmission path, said variations causing distortion, and a compensating path associated with saidtransmisequal to sion path comprising a plurality of equaliser sections having the same attenuation at zero frequency and attenuations at certain differing refence frequencies 101, 112, p3 pr equal to said attenuation at zero frequency multiplied by an arbitrary factor, said different reference frequencies being allotted to'said sections and thereby distributed in such a way as to correspond to a series of slowly or evenly varying differences of two functions F(p1-+1)F(pr), thereby substantially equalising'simultaneously said variations of attenuation and phase delay causing distortion, wherein the equaliser sections are arranged to constitute an artificial line arranged in series with said transmission path.

15. A wave transmission system including a transmission path along which oscillations extending over a range of frequencies are caused to travel and in which range the attenuation of said path varies with the frequency w substantially as the sum FM) of at least two terms of the form Anw", said magnitudes An and n to be determined by analysis of the characteristics of the transmission path, said variations causing distortion, and a compensating path associated with said transmission path comprising a plurality of equaliser sections having the same attenuation at zero frequency and attenuation at certain differing reference frequencies 111,102,123 pr equal to said attenuation at zero frequency multiplied by an arbitrary factor, said different reference frequencies being allotted to said sections and thereby distributed in such a way as to correspond to a series of slowly or evenly varying differences of two functions F(p1-+1)F(pr), thereby substantially equalisingsimultaneously said variations of attenuation causing distortion, a number N (p), of said reference frequencies being located per unit frequency range at frequency p where the co-efiicient C11. being the co-efiicientin a typi-' cal term of the characteristic EnCnw to be simulated substantially in order that said distortion may be equalised substantially and f(q) represents generally the loss characteristic of one of said sections, where q=P/w.

l6. A wave transmission system including a transmission path along which oscillations ex tending over a range of frequencies are caused to travel and in which range the attenuation of said path varies with the frequency w substantially as the sum F0) of at least two terms of the form Ana and the phase delay of said path varies substantially as the sum of at least two terms of the form A" tan 'nmw" said magnitudes An and n to be determinedby analysis of the characteristics of the transmission path, said variations causing distortion, and a compensating path associated with said transmission path comprising a [plurality of equaliser sections having the same attenuation at zero frequency andattenuation at certain differing reference frequencies m, 102, p3 p'r equal to said attenuation at zero frequency multiplied by an arbitrary factor, said different reference frequencies being allotted to said sections and thereby distributed in such a way as to correspond to a series'of slowly or evenly varying differences of two functions F(pr+1)F(pr), thereby substantially equalising simultaneously said variations of attenuation and phase delay causing distortion, wherein said equaliser sections are composed of series arms each including a resistance and inductance which in series are shunted by a condenser, and shunt arms each including a resistance in series with inductance, the resistance being shunted by a condenser.

1'7. A wave transmission system comprising a transmission path along which oscillations extending over a range of frequencies are caused to travel, in which the path is such as to introduce distortion of said signals and in which said distortion corresponds to a frequency characteristic F(w) of the form of at least two terms of the form Xnw" where w is the frequency of said oscillations and the magnitudes X and 1;, determined by analysis of the characteristics of the transmission path, and n is limited to values less than two if F(w) represents loss or to values less than unity if F0) represents phase delay and a compensating or equalising path associated with said transmission path formed by the connection in series of a plurality of equaliser sections having reference frequencies 101, 112, p3 pr allotted and being thereby distributed in such a way as to correspond to a series of slowly or evenly varying differences of two functions F(p1+1)F(pr) whereby said distortion of said signals is substantially compensated in said range of frequencies.

18. Means for simulating a predetermined frequency characteristic F(w) lying within a predetermined range of frequencies and of the form of at least two terms of the form Xnw" where w is the frequency and the magnitudes X and n determined by analysis of the characteristics of the transmission path, and n is limited to Values less than two if F0) represents loss or to values less than unity if F(w) represents phase delay comprising a plurality of sections which are connected in series to form a transmission path and which possess reference frequencies :21, 172, p3 pr so distributed as to correspond to a series of slowly or evenly varying differences of two functions F(pT+1) F (pr) whereby said transmission path possesses a frequency characteristic which simulates substantially said predetermined characteristic.

19. Means for simulating a predetermined frequency characteristic F(w) lying within a predetermined range of frequencies and of the form of at least two terms of the form Xnw" where w is the frequency and the magnitudes X and n determined by analysis of the characteristics of the transmission path, and n is limited to values less than two if F(w) represents loss or to values less than unity if F(w) represents phase delay comprising a plurality of sections which are connected in series to form a transmission path and which possess reference frequencies 121, 172, p3 pr so distributed as to correspond to a series of slowly orevenly varying differences of two functions F(I)r+1)-F(pr) whereby said transmission path possesses a frequency characteristic which simulates substantially said predetermined characteristic, wherein said sections are composed of series arms each including a resistance and inductance which in series are shunted by a condenser, and shunt arms each including a resistance in series with inductance, the resistance being shunted by a condenser.

20. Means for simulating a predetermined frequency characteristic F(w) lying within a predetermined range of frequencies and of the form of at least terms of the form Xnw" Where w is the frequency and the magnitudes X and 11. determined :by analysis of the characteristics of the transmission path, and n is limited to values less than two if F(w) represents loss or to values less than unity if F(w) represents phase delay comprising a plurality of sections which are connected in series to form a transmission path and which possess reference frequencies 111, 122, pa 1J1- so distributed as to correspond to a series of slowly or evenly varying differences of two functions F(p1-+1) -F(pr) whereby said transmission path possesses a frequency characteristic which simulates substantially said predetermined characteristic, wherein said sections are composed of shunt arms each including a resistance and inductance which in series are shunted by a condenser, and series arms each including a resistance in series with inductance, the resistance being shunted by a condenser.

JOHN COLLARD. JOHN EDWARD BEST.

CERTIFICATE OF CORRECTION. Patent No. 2,2Lf2,87'9. May 20, 19M.

JOHN COLLARD, ET AL. I It ishereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 6, first column, line b], claim 2, for the word "relay" read \delay-; line 61,

same claim, for "difference" read different; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 17th day of June A. D. 19141.

Henry Van Arsdale (Seal) Acting Commissioner of Patents. 

